This invention relates to a heating system for swimming pools and in particular to such a system which utilizes a heat pump.
In the past electricity has been the predominant energy source for heating swimming pools, due to its being a readily available and clean source of energy. In the past when electrical energy has been used for this purpose, it has normally been used in the form of resistance heating, however, resistance heating is inefficient and as the cost of electrical power increases it becomes increasingly desirable to use other, more efficient, types of electrical heating, such as a heat pump. Even though heat pumps are relatively efficient means of utilizing electrical energy for heating they have certain operating characteristics which seriously limit their use for heating swimming pools. In the operation of a heat pump it is imperative that the pressure of the heat transfer fluid as it is discharged from the heat pump remain relatively constant. Otherwise the heat pump will often be operating in a range where its efficiency is significantly reduced. This characteristic of heat pumps is not a serious limitation when they are used for space heating since the heat capacity of the air being heated is much lower than that of the heat transfer fluid. Therefore, even when the space being heated becomes quite cool, the discharge pressure, is not overly effected. In addition, even if the discharge temperature of the heat transfer fluid is reduced below the desirable range, the space is raised to the desired temperature rather quickly and then kept at a relatively constant temperature. Therefore, any effect temperature has on operating efficiency of the heat pump is of short duration and thus of little importance.
On the other hand, the water being heated in a swimming pool has a much larger heat capacity than air. Therefore, when cool water is being heated it is much more likely to cause the discharge temperature of the heat transfer fluid to drop than is the case with air. Furthermore, it typically takes a much longer time to heat a cool swimming pool than a cool house and accordingly the heat pump will be forced to operate in an inefficient mode for a much longer period of time in the former case than in the latter.
What is needed, therefore, is a means for automatically regulating the discharge pressure of the heat transfer fluid in a heat pump when the heat pump is used for heating a swimming pool, so that the heat pump always operates within its desired range.
The heating system of the present invention serves this end by continuously regulating the amount of pool water which is subjected to being heated by the heat pump, thereby causing the heat pump to be operated at a constant discharge pressure.
The heating system of the present invention includes a system bypass line, which is connected to the pool outlet line, to divert a portion of the pool water to the heating system. A manually operable diverter valve located in the pool return line ensures that a controlled amount of water is so diverted. The diverted portion of the pool water is then passed through the secondary coil of a commercially available heat exchanger which has the heated heat transfer fluid from the heat pump being circulated through its primary coil.
The regulating element consists of a three-way regulator valve which is located in the system bypass line upstream of the heat exchanger. The regulator valve is connected so that its inflow port receives pool water from the pool, a first outlet port discharges water into a regulator return line which is connected to the pool return and a second outflow port discharges water back into the pool bypass line for passage to the heat exchanger. The position of the regulator valve is responsive to the discharge pressure of the heat transfer fluid through operation of control means so that if the pool water causes undue cooling of the heat transfer fluid from the heat pump, therefore causing its temperature, and thus its pressure, to drop, the regulator valve will direct a greater portion of the pool water out of its first outflow port thus correcting this effect. On the other hand, when the discharge pressure of the heat transfer fluid increases, a greater portion of the pool water is passed out of the second outflow port to the heat exchanger. As a result, the discharge pressure remains relatively constant and within the range where the heat pump operates more efficiently. While the regulator valve maintains the heat pump within its desired range, a separate thermostatically controlled switch located in the pool outlet line causes the heat pump to initiate and terminate operation responsive to pool demand.
One drawback of using a regulator valve of this type is that it operates to eliminate any heating load from being available when the heat pump is reversed to defrost its evaporator coil. In this event as the heat transfer fluid passing to the heat exchanger becomes cooled, since in this configuration the heat pump is operating as a refrigeration unit, the regulator valve would normally respond by directing an increasingly greater portion of the pool water through the regulator return line rather than through the heat exchanger. Thus there would be increasingly less pool water available to serve as a heat source for the heat pump as it continued in its defrost cycle.
In the present invention this problem is solved by placing a defrost bypass line between the inflow and second outflow ports of the regulator valve and placing a solenoid-operated first bypass control valve in the bypass line. In addition, a solenoid-operated second bypass control valve is located in the regulator return line. Accordingly, the bypass control valves are annunciated by the heat pump controls so that during defrost the first valve is opened and the second valve is closed. As a result, all of the pool water is directed through the heat exchanger to act as the heat source for the heat pump.
Accordingly, it is a principal object of the present invention to provide a system for heating a swimming pool with a heat pump wherein the discharge pressure of the heat transfer fluid in the heat pump automatically remains within a predetermined range at all times.
It is a further object of the present invention to provide such a system wherein the heat pump can also be operated in a defrost cycle.
It is a further object of the present invention to provide such a system which is operated on a demand basis responsive to pool temperature.
It is a still further object of the present invention to provide such a system having an emergency shutdown which terminates operation of the heat pump in the event the flow of pool water is discontinued or severely curtailed.
The foregoing and other objectives, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.